The present invention relates to a method for checking a knocking device according to the present invention, and to a device for carrying out the method.
Conventional garbage incineration plants have, as a rule, at least one boiler which generates steam or hot water which can be used for generating electrical current or for heating households. Depending on whether steam or hot water is primarily generated in the boiler, this is also designated as a steam generator or as a hot water generator.
Steam or hot water generation takes place by means of heat exchanger elements which are arranged inside the boiler housing. Said heat exchanger elements are present in the convection flues, as they are known, as a rule in the form of tube bundles (also designated as “harps”), the tubes of which have water or steam flowing through them and issue into a header. At these tube bundles, heat is transferred from the hot smoke gas to the water or steam which is thereby heated, evaporated or superheated. Heat transmission takes place primarily by convection in such tube bundles.
However, the surface of these heat exchanger elements is heavily contaminated by the deposition of fly ash entrained in the smoke gas. This contamination or slagging reduces the transfer of heat to the water or steam and therefore leads, overall, to reduced efficiency of the boiler.
Moreover, since the smoke gas cross section is narrowed as a result of the deposits, the pressure loss increases and may lead to the complete clogging of the smoke gas cross section. Further, the maintenance measures required as a result entail high costs and losses of output.
Overall, the contamination or slagging of the heat exchanger elements therefore reduces the “running time” of the boiler (that is to say, the time in which the boiler can operate under the highest safeguarded load, while maintaining all the safeguarded properties, without maintenance being necessary) and, consequently, also the availability of the garbage incineration plant (that is to say, the ratio of the operating time of the plant plus the reserve time to the nominal operating time).
This problem is dealt with, in practice, by cleaning off the surface of the heat exchanger elements while the boiler is in operation. Methods of various types may be considered for this purpose. For example, the surface of the heat exchanger elements may be cleaned off by means of a soot blower, a water spraying plant, a shot peening plant or a knocking device.
In the case of horizontal boiler flues of a garbage incineration plant, the heat exchanger elements are designed, as a rule, as suspendedly arranged tube bundles. For cleaning of such suspended tube bundles, in particular, knocking devices are highly appropriate. In this case, the contaminated tube bundles are set in oscillation by means of a pulse, the incineration residues which adhere to the surface falling off. The pulse is imparted, as a rule, via a knocking ram which, depending on the situation, is actuated by a mechanically driven hammer or by a pneumatic impact cylinder. In general, the impact of the knocking ram takes place on the header of the tube bundle.
Examples of knocking devices are described in the prior art.
Thus, for example, DE 27 10 153 describes the use of an oscillation generator, designed as a knocking device with a knocking cylinder, for cleaning the heating surface of a steam generator.
Further, DE 198 53 715 describes a knocking device for cleaning off tube coils of boiler plants.
The cleaning success of such knocking devices depends in this case on a multiplicity of factors. In addition to the impact energy and the impact frequency, in particular, the oscillation behavior and the suspension of the tube bundles are also of critical importance. Before the boiler of the garbage incineration plant is commissioned, therefore, a check is made, in practice, as to whether the knocking rams of the knocking device impinge onto the location desired in each case and set the tube bundles in oscillation in the desired way.
However, the conditions before the commissioning of the boiler differ very sharply from those during operation, particularly with regard to the operating temperature and the degree of contamination. This, in practice, presents the problem that, even when a check is conducted before commissioning, the operating capacity of the knocking device, that is to say the application of the desired pulse to the heat exchanger element, is often not ensured in full during operation. There is a multiplicity of possible reasons for this. For example, the lack of operating capacity may be due to the fact that the knocking ram is severely warn or is subjected to high friction in the guide through the wall of the boiler housing. Further, it is conceivable, for example, that the heat exchanger element may become jammed during operation and is therefore no longer in its position of rest before commissioning, with the result that an optimal impingement of the knocking ram on the heat exchanger elements is impaired, etc.
No suitable methods have been described hitherto for checking the knocking device while the boiler is in operation. However, it is precisely a check of the knocking device during operation which would be very useful, since only reliable information of this kind makes it possible to ascertain how far the operating capacity of the knocking device is impaired during operation and exactly where maintenance work would have to be carried out.